fix(voice): accept string dtype settings

[Hughhhhcoder]

Summary

• normalize TTS output dtypes with NumPy before selecting the supported int16/float32 conversions
• accept JSON/dictionary string spellings such as "int16" and "float32"
• preserve UserError("Invalid output dtype") for unsupported or invalid dtypes

Fixes #4777

Validation

• .venv/bin/pytest -q tests/voice/test_pipeline.py (58 passed)
• .venv/bin/ruff check src/agents/voice/result.py tests/voice/test_pipeline.py
• .venv/bin/ruff format --check src/agents/voice/result.py tests/voice/test_pipeline.py
• .venv/bin/pyright --project pyrightconfig.json src/agents/voice/result.py tests/voice/test_pipeline.py
• git diff --check

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T07:13:56.358070Z	65d5cd3	Manual request
🔒 Security Review	✅ Completed 2026-08-31T07:16:05.304058Z	65d5cd3	Manual request

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[Hughhhhcoder]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: 65d5cd3cf6

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[chatgpt-codex-connector]

Security review completed. No security issues were found in this pull request.

Reviewed commit: 65d5cd3cf6

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[Hughhhhcoder]

Closing in favor of #4778, which predates this PR and covers the same dtype normalization behavior with broader regression coverage. Thanks to @ErenAta16 for the careful side-by-side comparison.